netdev - RE: [PATCH net v2] iavf: Detach device during reset task

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Date:   Tue, 30 Aug 2022 20:49:54 +0000
From:   "Laba, SlawomirX" <slawomirx.laba@...el.com>
To:     ivecera <ivecera@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "Keller, Jacob E" <jacob.e.keller@...el.com>,
        "Piotrowski, Patryk" <patryk.piotrowski@...el.com>,
        Vitaly Grinberg <vgrinber@...hat.com>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        "moderated list:INTEL ETHERNET DRIVERS" 
        <intel-wired-lan@...ts.osuosl.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net v2] iavf: Detach device during reset task

> -----Original Message-----
> From: Ivan Vecera <ivecera@...hat.com>
> Sent: Tuesday, August 30, 2022 10:16 AM
> Subject: [PATCH net v2] iavf: Detach device during reset task
> 
> iavf_reset_task() takes crit_lock at the beginning and holds it during whole call.
> The function subsequently calls
> iavf_init_interrupt_scheme() that grabs RTNL. Problem occurs when userspace
> initiates during the reset task any ndo callback that runs under RTNL like
> iavf_open() because some of that functions tries to take crit_lock. This leads to
> classic A-B B-A deadlock scenario.
> 
> To resolve this situation the device should be detached in
> iavf_reset_task() prior taking crit_lock to avoid subsequent ndos running under
> RTNL and reattach the device at the end.
> 
> Fixes: 62fe2a865e6d ("i40evf: add missing rtnl_lock() around
> i40evf_set_interrupt_capability")
> Cc: Jacob Keller <jacob.e.keller@...el.com>
> Cc: Patryk Piotrowski <patryk.piotrowski@...el.com>
> Cc: SlawomirX Laba <slawomirx.laba@...el.com>
> Tested-by: Vitaly Grinberg <vgrinber@...hat.com>
> Signed-off-by: Ivan Vecera <ivecera@...hat.com>
>
> @@ -2884,7 +2889,7 @@ static void iavf_reset_task(struct work_struct *work)
>  		if (adapter->state != __IAVF_REMOVE)
>  			queue_work(iavf_wq, &adapter->reset_task);
> 
> -		return;
> +		goto reset_finish;
>  	}
> 
>  	while (!mutex_trylock(&adapter->client_lock))

Ivan, what do you think about this flow [1]? Shouldn't it also goto reset_finish label?

	if (i == IAVF_RESET_WAIT_COMPLETE_COUNT) {
		dev_err(&adapter->pdev->dev, "Reset never finished (%x)\n",
			reg_val);
		iavf_disable_vf(adapter);
		mutex_unlock(&adapter->client_lock);
		mutex_unlock(&adapter->crit_lock);
		return; /* Do not attempt to reinit. It's dead, Jim. */
	}

I am concerned that if the reset never finishes and iavf goes into disabled state, and then for example if driver reload operation is performed, bad things can happen.

[1] https://elixir.bootlin.com/linux/v6.0-rc3/source/drivers/net/ethernet/intel/iavf/iavf_main.c#L2939